I think “moral responsibility” is a much more general term. Rome had a morality they were imposing on the world, so did Persia, or Charles Martel, or whoever. My reading is always just replace the word “moral responsibility” with “power” in the context of war, because in the context of war there is no difference in definition. Stream-of-consciousness key words here would be “manifest destiny”, “Mandate of Heaven”, “divine right”.

Modern concepts of warfare much more advance and based of sophisticated models. War viewed as network of continuous long term struggles. In US modern war concepts started with this book:

The Sling and the Stone: On War in the 21st Century (Zenith Military Classics)

Analysis based only on historical parallels hardly can provide adequate perception of current affairs. Modern wars is essentially special operation forces wars. US army has special forces in 165 countries. US is capable fighting few wars in different regions simultaneously and continuously. No one empire in the world history possessed such capabilities before. Also it would be naive to think that all that war machine is just for keeping piece.

The pitfall of many a modern political theory, which is to say limit on political thought, is that we assume the enemy of our enemy is our friend. In politics there are no friends, just those in the group, and those without.